Temporarily declare a variable in Bash
up vote
1
down vote
favorite
To declare a variable in Bash (say in a Bash script-file and not in Bash function) I do for example:
x=y
But when I finish using it inside that script-file I do unset x.
Is there a way (without using a function), to unset the variable after say 5 minutes, both in one line?
A plausible approach might be x=y && echo "unset x" | at now + 5 minutes.
bash variable at
asked 2 hours ago
JohnDoea
691132
add a comment |
up vote
1
down vote
favorite
To declare a variable in Bash (say in a Bash script-file and not in Bash function) I do for example:
x=y
But when I finish using it inside that script-file I do unset x.
Is there a way (without using a function), to unset the variable after say 5 minutes, both in one line?
A plausible approach might be x=y && echo "unset x" | at now + 5 minutes.
bash variable at
asked 2 hours ago
JohnDoea
691132
1
You need to dounset xonly if you are sourcing the script file. Otherwise the script runs in a subshell and does not affect your shell environment, so you don't need to unset it. I use parentheses to run one-liners with temporary variables on the command line all the time, like( for i in {1..20}; do dosomething; done), and after I execute this command I don't have$iin my shell.
– Weijun Zhou
47 mins ago
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
To declare a variable in Bash (say in a Bash script-file and not in Bash function) I do for example:
x=y
But when I finish using it inside that script-file I do unset x.
Is there a way (without using a function), to unset the variable after say 5 minutes, both in one line?
A plausible approach might be x=y && echo "unset x" | at now + 5 minutes.
bash variable at
asked 2 hours ago
JohnDoea
691132
To declare a variable in Bash (say in a Bash script-file and not in Bash function) I do for example:
x=y
But when I finish using it inside that script-file I do unset x.
Is there a way (without using a function), to unset the variable after say 5 minutes, both in one line?
A plausible approach might be x=y && echo "unset x" | at now + 5 minutes.
bash variable at
bash variable at
asked 2 hours ago
JohnDoea
691132
asked 2 hours ago
JohnDoea
691132
asked 2 hours ago
JohnDoea
691132
asked 2 hours ago
JohnDoea
691132
asked 2 hours ago
JohnDoea
691132
691132
1
You need to dounset xonly if you are sourcing the script file. Otherwise the script runs in a subshell and does not affect your shell environment, so you don't need to unset it. I use parentheses to run one-liners with temporary variables on the command line all the time, like( for i in {1..20}; do dosomething; done), and after I execute this command I don't have$iin my shell.
– Weijun Zhou
47 mins ago
add a comment |
1
You need to dounset xonly if you are sourcing the script file. Otherwise the script runs in a subshell and does not affect your shell environment, so you don't need to unset it. I use parentheses to run one-liners with temporary variables on the command line all the time, like( for i in {1..20}; do dosomething; done), and after I execute this command I don't have$iin my shell.
– Weijun Zhou
47 mins ago
1
1
You need to do
unset x only if you are sourcing the script file. Otherwise the script runs in a subshell and does not affect your shell environment, so you don't need to unset it. I use parentheses to run one-liners with temporary variables on the command line all the time, like ( for i in {1..20}; do dosomething; done), and after I execute this command I don't have $i in my shell.– Weijun Zhou
47 mins ago
You need to do
unset x only if you are sourcing the script file. Otherwise the script runs in a subshell and does not affect your shell environment, so you don't need to unset it. I use parentheses to run one-liners with temporary variables on the command line all the time, like ( for i in {1..20}; do dosomething; done), and after I execute this command I don't have $i in my shell.– Weijun Zhou
47 mins ago
add a comment |
2 Answers
2
active
oldest
votes
up vote
4
down vote
You can't use at jobs because they run in a different context, and can't affect the current shell.
But we can do something similar. This code will trigger an alarm signal, which we can catch and perform action on
#!/bin/bash
x=100
trap 'unset x' SIGALRM
mypid=$$
( /bin/sleep 3 ; kill -ALRM $mypid) &
for a in 1 2 3 4 5 6
do
echo Now x=$x
sleep 1
done
This example is only 3 seconds long to demonstrate the solution; you can pick your delay as you need.
In action:
Now x=100
Now x=100
Now x=100
Now x=
Now x=
Now x=
You can easily make it one line with ;...
answered 1 hour ago
Stephen Harris
23.9k24477
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
1
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean theforloop won't demonstrate the solution working. I'll edit the answer to make that clear.
– Stephen Harris
1 hour ago
add a comment |
up vote
3
down vote
Sure:
trap 'unset x; trap - USR1' USR1; { sleep 5m; kill -USR1 $$; } &
This sets a trap on the USR1 signal, then (cheating with a semicolon to put it on one line) groups together the sleep and kill commands into a background job. When that job completes, it will send the USR1 signal to the current shell, which will execute the trap. The trap unsets x and then clears the trap.
No functions!
answered 1 hour ago
Jeff Schaller
37.6k1052121
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
You can't use at jobs because they run in a different context, and can't affect the current shell.
But we can do something similar. This code will trigger an alarm signal, which we can catch and perform action on
#!/bin/bash
x=100
trap 'unset x' SIGALRM
mypid=$$
( /bin/sleep 3 ; kill -ALRM $mypid) &
for a in 1 2 3 4 5 6
do
echo Now x=$x
sleep 1
done
This example is only 3 seconds long to demonstrate the solution; you can pick your delay as you need.
In action:
Now x=100
Now x=100
Now x=100
Now x=
Now x=
Now x=
You can easily make it one line with ;...
answered 1 hour ago
Stephen Harris
23.9k24477
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
1
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean theforloop won't demonstrate the solution working. I'll edit the answer to make that clear.
– Stephen Harris
1 hour ago
add a comment |
up vote
4
down vote
You can't use at jobs because they run in a different context, and can't affect the current shell.
But we can do something similar. This code will trigger an alarm signal, which we can catch and perform action on
#!/bin/bash
x=100
trap 'unset x' SIGALRM
mypid=$$
( /bin/sleep 3 ; kill -ALRM $mypid) &
for a in 1 2 3 4 5 6
do
echo Now x=$x
sleep 1
done
This example is only 3 seconds long to demonstrate the solution; you can pick your delay as you need.
In action:
Now x=100
Now x=100
Now x=100
Now x=
Now x=
Now x=
You can easily make it one line with ;...
answered 1 hour ago
Stephen Harris
23.9k24477
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
1
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean theforloop won't demonstrate the solution working. I'll edit the answer to make that clear.
– Stephen Harris
1 hour ago
add a comment |
up vote
4
down vote
up vote
4
down vote
You can't use at jobs because they run in a different context, and can't affect the current shell.
But we can do something similar. This code will trigger an alarm signal, which we can catch and perform action on
#!/bin/bash
x=100
trap 'unset x' SIGALRM
mypid=$$
( /bin/sleep 3 ; kill -ALRM $mypid) &
for a in 1 2 3 4 5 6
do
echo Now x=$x
sleep 1
done
This example is only 3 seconds long to demonstrate the solution; you can pick your delay as you need.
In action:
Now x=100
Now x=100
Now x=100
Now x=
Now x=
Now x=
You can easily make it one line with ;...
answered 1 hour ago
Stephen Harris
23.9k24477
You can't use at jobs because they run in a different context, and can't affect the current shell.
But we can do something similar. This code will trigger an alarm signal, which we can catch and perform action on
#!/bin/bash
x=100
trap 'unset x' SIGALRM
mypid=$$
( /bin/sleep 3 ; kill -ALRM $mypid) &
for a in 1 2 3 4 5 6
do
echo Now x=$x
sleep 1
done
This example is only 3 seconds long to demonstrate the solution; you can pick your delay as you need.
In action:
Now x=100
Now x=100
Now x=100
Now x=
Now x=
Now x=
You can easily make it one line with ;...
answered 1 hour ago
Stephen Harris
23.9k24477
edited 1 hour ago
answered 1 hour ago
Stephen Harris
23.9k24477
answered 1 hour ago
Stephen Harris
23.9k24477
answered 1 hour ago
Stephen Harris
23.9k24477
23.9k24477
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
1
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean theforloop won't demonstrate the solution working. I'll edit the answer to make that clear.
– Stephen Harris
1 hour ago
add a comment |
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
1
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean theforloop won't demonstrate the solution working. I'll edit the answer to make that clear.
– Stephen Harris
1 hour ago
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
Wow - great minds think alike -- and within 30 seconds of each other! :)
– Jeff Schaller
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
@JeffSchaller I noticed that :-)
– Stephen Harris
1 hour ago
1
1
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean the
for loop won't demonstrate the solution working. I'll edit the answer to make that clear.– Stephen Harris
1 hour ago
@JeffSchaller I rolled back your edit; I specifically put a 3 second pause in as an example; a 300 second (5minute) sleep would mean the
for loop won't demonstrate the solution working. I'll edit the answer to make that clear.– Stephen Harris
1 hour ago
add a comment |
up vote
3
down vote
Sure:
trap 'unset x; trap - USR1' USR1; { sleep 5m; kill -USR1 $$; } &
This sets a trap on the USR1 signal, then (cheating with a semicolon to put it on one line) groups together the sleep and kill commands into a background job. When that job completes, it will send the USR1 signal to the current shell, which will execute the trap. The trap unsets x and then clears the trap.
No functions!
answered 1 hour ago
Jeff Schaller
37.6k1052121
add a comment |
up vote
3
down vote
Sure:
trap 'unset x; trap - USR1' USR1; { sleep 5m; kill -USR1 $$; } &
This sets a trap on the USR1 signal, then (cheating with a semicolon to put it on one line) groups together the sleep and kill commands into a background job. When that job completes, it will send the USR1 signal to the current shell, which will execute the trap. The trap unsets x and then clears the trap.
No functions!
answered 1 hour ago
Jeff Schaller
37.6k1052121
add a comment |
up vote
3
down vote
up vote
3
down vote
Sure:
trap 'unset x; trap - USR1' USR1; { sleep 5m; kill -USR1 $$; } &
This sets a trap on the USR1 signal, then (cheating with a semicolon to put it on one line) groups together the sleep and kill commands into a background job. When that job completes, it will send the USR1 signal to the current shell, which will execute the trap. The trap unsets x and then clears the trap.
No functions!
answered 1 hour ago
Jeff Schaller
37.6k1052121
Sure:
trap 'unset x; trap - USR1' USR1; { sleep 5m; kill -USR1 $$; } &
This sets a trap on the USR1 signal, then (cheating with a semicolon to put it on one line) groups together the sleep and kill commands into a background job. When that job completes, it will send the USR1 signal to the current shell, which will execute the trap. The trap unsets x and then clears the trap.
No functions!
answered 1 hour ago
Jeff Schaller
37.6k1052121
edited 1 hour ago
answered 1 hour ago
Jeff Schaller
37.6k1052121
answered 1 hour ago
Jeff Schaller
37.6k1052121
answered 1 hour ago
Jeff Schaller
37.6k1052121
37.6k1052121
add a comment |
add a comment |
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1
You need to do
unset xonly if you are sourcing the script file. Otherwise the script runs in a subshell and does not affect your shell environment, so you don't need to unset it. I use parentheses to run one-liners with temporary variables on the command line all the time, like( for i in {1..20}; do dosomething; done), and after I execute this command I don't have$iin my shell.– Weijun Zhou
47 mins ago